There are many diagnostic tools which can help physician to detect and localize the diseased tissues. Many diseased tissues are detected by the physical properties measured by imaging modalities, but many diseases may go undetected. Magnetic resonance elastography (MRE) can cover those undetected diseases such as early detection of small tumor, carcinoma, cirrhosis, arteriosclerosis, lymphedema, mild cognitive impairment (MCI) or related brain diseases, or FDA new drug testing in the below-mentioned ways.
MRE detects “atomic density change” with very high resolution. Diseased tissue changes its “elasticity” and “density” before its “shape change.” Elastography can detect either “elasticity change” or “density change” of tissues before “shape change”. MRE can detect diseased tissue before its “shape change”, which can be detected using other diagnostic tools such as X-ray, CT, ultrasound, PET and magnetic resonance imaging (MRI). MRE can detect diseased tissue before its “function, enzymes, chemistry, electrolytes, lipids and protein changes”, which can be detected by blood tests such as liver function, liver enzymes, liver chemistry, liver electrolytes, liver lipids and liver protein. Early detection improves effectiveness of treatments. MRE improves early detection capability including (a) small size of “shape changes”; (b) some other physical property changes before “shape changes”; (c) some other physical property changes before “function, enzymes, chemistry, electrolytes, lipids and protein changes”; and (d) small size of “some other physical property changes”.
Historically, one of the physician's most valuable diagnostic tools is palpation. By palpating the patient a physician can feel differences in the compliance of tissues and detect the presence of tumors and other tissue abnormalities. Unfortunately, this valuable diagnostic tool is limited to those tissues and organs which the physician can feel, and many diseased internal organs go undiagnosed unless the disease happens to be detectable by one of the conventional imaging modalities. The stiffness of tumors, (e.g. of the liver and the brain) which are undetected by existing imaging modalities and cannot be reached for palpation through the patient's skin and musculature, are often detected by surgeons by direct palpation of the exposed organs at the time of surgery. Palpation is the most common means of detecting enlargement of lymph glands and tumors of the prostate gland and the breast. Unfortunately, deeper portions of these structures are not accessible for such evaluation. An imaging system that extends the physician's ability to detect differences in tissue compliance throughout a patient's body would extend this valuable diagnostic tool.
MRI can be enhanced when an oscillating stress is applied to a subject being imaged by MRE method. The method requires that the oscillating stress produce shear waves that propagate through the organ, or tissues to be imaged. These shear waves alter the phase of the nuclear resonance imaging (NMR) signals, and from this the mechanical properties of the subject can be determined. In many applications, the production of shear waves in the tissues is merely a matter of physically vibrating the surface of the subject with an electromechanical device. For example, shear waves may be produced in the breast and prostate by direct contact with the oscillatory device. Also, with organs like the stomach and uterus, the oscillatory force can be directly applied by means of an applicator that is inserted into the organ.
MRE early detection depends on its driver. A number of driver devices have been developed to produce the oscillatory force needed to practice MRE. Electromechanical driver devices typically include a coil of wire through which an oscillating current flows. To create an oscillating current flow, the coil has to be oriented in the polarizing magnetic field of a MRI system to avoid the interactions with the magnetic field. The force of oscillating current flows may be conveyed to the subject being imaged by any number of different mechanical arrangements. Such MRE drivers can produce large forces over large displacement, but they are constrained by the need to keep the coil properly aligned with respect to the polarizing magnetic field. In addition, the current flowing in the driver coil produces a magnetic field which can alter the magnetic fields during the magnetic resonance pulse sequence resulting in undesirable image artifacts. It is also easy to burn out during the magnetic resonance (MR) scan due to the eddy current, especially in the higher field MR system such as in a 3 T MR system.
Another approach is the employment of piezoelectric drivers. Piezoelectric drivers can also be oriented in any direction since they are not dependent on the polarizing magnetic field direction for proper operation. Such drivers do not produce troublesome disturbances in the scanner magnetic fields when operated, but they are limited in the forces they can produce, particularly at larger displacements. It's easy to break under increased force due to the thin and brittle material.
A further approach is the employment of pneumatic drivers. Pneumatic driver produces large forces and can be oriented in any direction inside the MR system. While there are no artifacts, it is hard to put in the position due to the hard tube and hard passive actuator. A subject will feel very uncomfortable when putting the hard passive actuator on some regions of the subject, especially for the brain. The stimulation frequency and power at the end of the pneumatic driver are unknown. Also, the power is attenuated seriously due to the long tube.
The above description of the background is provided to aid in understanding the hydraulic driver for magnetic resonance elastography disclosed in the present application, but is not admitted to describe or constitute pertinent prior art to the hydraulic driver for magnetic resonance elastography, or consider any references as material to the patentability of the claims of the present application.